Method for locating hydrocarbon deposits in the earth



Sept. 30, 1941. G. HOWELL METHOD FOR LOCATING HYDROCAR. 31 DEPOSITS IN THE EARTH Original Filed Dec. 27, 1934 1 L 1 M/ U W 0 u u U fl adjacent 'a stratum containing' petroleum oil and/or natural gas contain measurable amounts of methane, ethane and sometimes butane and propane. Ethane is present in the soil gases above oil and/or natural gas deposits in a convarying amounts. It is seen therefore that the positive identification of ethane in a gas sample- ;obtained from the soil is an indication of the i presence of a deposit of oil or natural gas below j .the point 'at which the gas sample was obtained.

The hydrocarbons absorbed in the solvent are therefore analyzed for hydrocarbons heavier than methane, more particularly ethane and pos- E j sibly butane and propane.

analyzing the hydrocarbons In one method of the ethyl alcohol is 'subjected to elevated temperatures until the gases dissolved in the alcohol have been evaporated. 1 These gases'are then cooled to about -40 C.

whereby some of the gases are liquefied and this i liquid is drained off. The liquid is mostly alcohol but some of the heavier hydrocarbons if present will also liquefy at this temperature. The

i remaining gases are then cooled off below the boiling point ofethane. The liquid ethane is then drained off and measured. I

In making a survey, the boreholes 2 may be disposed approximately 500 to 1500 feet apart, although greater and smaller separations may be employed in different areas. Reconnalssance i surveys using the greater separation of boreholes have been found advisable. Those areas which are found to have soils of high hydrocarbon and especially ethane content are then Referring to Fig. 3; a modified form of the invention is shown in which i, I' designate the surface of the ground. A tubular member 35 is provided with an open end adaptedto be forced into the ground for a suflicient distance to form good contact all around the end of the tubular member 35 with the ground. The upper end oi! th tubular member 35 is closed as indicated et' I& forming a reservoir 31 which opens upon the ground. As shown in its preferred embodiment, the tubular member has the form of a bell jar. Preferably it has a diameter of from three to five feet. A convenient' method oi' sealing it with respect to the ground is to rotate the tubulamember untfl it makes good contact with the ground. 'Plaster of Paris or other suitable scaling means designated 39 is then poured around the circumference of the tubular member 35 to form a good seal to prevent themtrance of surface I air into the reservoir 31. Means are provided for` drawing soll gases 'from the ground into the-reservoir 31 identical 'in all respects with the means illustrated in'Fig. 1 and like reference numerals are applied to like parte'. The means comprises a pump having an inlet plpe 24 whichopens into the upper portion of acontainer 20 partially filled with suitable solvent or., hydroca'rbons such as. ethyl alcohol. Glass heads 30 or the like are disposed in the solvent. e A pipe I! protrudes into the reservoir, 31 at one end and at its other end opens into the worked in greater detail with the boreholes closer' together.

. focused on container 26 below the level of the solvent therein.

8 fer from the serious disadvantages that rather large samples are required and the sensitivity is low. It is impossible byvthese methods to work with an accuracy much greater than 0.1 of 1%. Thus ethane must be present to the extent of one part in about 1,000 parts of gas. Soil gas samples rarely contain such an abundance of p ethane.

The third method of analysis by 'means of canal or positive rays permits of the deflnite identification of the different hydrocarbons in of' estimating their relative this method-the gas molecules the sample and abundancies. In I are shot at a photographicplat by means of an electric accelerating field through crossed electric and magnetic fields. 'The molecules sufler a deflection in both elds, 'the detj lectio n in the electric field being proportional to and in the magnetic field i v where 5 e=elementary charge :electric field strength m=molecular weight H=nagnetic field strength v=velocity of molecule Molecules of the same molecular weight are the-same spot on th photographie plate. The resolution is very high. being about one part in one thousand parts.. This means .that particles 'having weights of 100.0 and 1004, respectively, can be separated. In the present case. the molecular weight of methane is '16,04, of ethane 30.06, of propane 44.08 and of butane 58.10.' Therelative amount 'of each constituent of the sample isjestimated from the intensities of the different Spots or The emission or llnes on the photographic absorption spectral analysis can also be used to detect hydrocarbons in the soil gases.

The flfth method-is based on the fact that the' dielectric' constants of these gases are markedly that they also have different mag- 'tric constants increase in the order` air. methan'e.

` ethane,'propane, butane, while the magnetic sus oeptibili ties decrease in the same order; It is seen therefore that if higher if methane. were substituted for the air. and progressively higher for -ethane, propane the presenceof the a sample of air were plaoed between the plates of, a condenser and inside the coil of' an eleetric oscillating 'tuned to a; .v certain high frequen'cy, say one or 'several million cycles, the frequency of' 'the system' would be* minimum of light intensity at 2,257,17o and butane. The circuit comprising this condenser and coll can be caused to beat against another crystal controlled. circuit. now that the crystal controlled circuit be caused to oscillate at five million cycles and that the first circuit be tuned to thesame i-equency when air has been placed between the condenser plates and inside oi the coi, it is easy to see that the accuracy would be as great as one part in five million, since a beat irequency of one cycle per second could be observed easily. If, therefore, the substitution oi'. the soil gas sample for the air would change the frequency of the circuit by one cycle, the change could be observed. It is known also that the ratio of methane to ethane in natural gas is about eight to one. The apparatus can thereiore be caibrated with samples known to contain certain amounts of methane and ethane. v

Another highly desirable method' is the magneto-optic due to F. Allison. It'is possible to detect one part in one hundred billion by means of this arrangement. The method which is described in the literature, tor instance in Physical Review, volume 30, page 66, 1927,\volume 31, page 313, 1928, and volume 35,` page 124, 1930, and elsewhere, is based on the time lag difl'erences of the Faraday eflect behind the magnetic field in liquids as a function oi' the chemical compounds dissolved in the liquid. The soll gases are passed through alcohol. The hydrocarbons are'soluble in the alcohol while oxygen and niti-agen are 1nsoluble. The alcohol solution containing the dissolved hydrocarbons is then analyzed. Each chemica compound produces a characteristic a certain length of light path. These minimo. disappear when the concentration is less than one part in one hundred billion parts. Since ethane is present in the soil gases over deposits ot oil and/or natural gas in greater conceiirations, it is seen that the magneto-optic method is amply sensitive !or its positive identification. v

This application is a division oi' my eopending app ication, Serial Number ?59,373, filed December 27, 1934. 4

various changes may be made within the scope o! the appended claims in which it is desired 'to claim all novelty inherent in the invention as broadly as the prior art permits.

1. In the method oi prospecting for petroleum deposits in which a sample oi' soil gas is obtained and examined for hydrocarbons higher than methane, the steps of obtaining a sample which comprises sucking gas from the soil, passing a predetermined quantity oi the gas through a liquid having a high absorption power !or low molecular weight hydrocarbons as compared to its absorption power for other constituents ot soll gas and recovering said hydrocarbons from said liquid. 2. In the method orprospecting for petroleum deposits in which 'a sample oi soil gas is obtained and examined for hydrocarbons higher than methane, the steps oi' procuring a sample which comprises establishing a zone in the earth free for the atmosphere, sucking gas out or said I zone, measuring the volume oi' said gas,`

it through a liq'uid having high absorption power for gaseous hydrocarbons as compared with its absorption power for other constituents of soil gas and recovering said hydrocarbons rrom said liquid.

3. In the method of prospecting for petroleum deposlts by procuring a sample oi' soll gas and examining it for hydrocarbons higher than methane, the steps which comprise absorbing the hydroc'arbon content of a sample ot soil'gas or known volume by passing the gas through a liquid high absorption power tor hydrocarbons as compared to its absoi-ption power tor other constit'uents orthe gas, separating said hydrocarbons from the absorption liquid, subjecting the separated hydrocarbons to a temperatu-e below the boiling point or ethane but above the boiling having a LYNN G. noma.,

point oi' methane, recovering the oon- -densed hydroearbons and analyzing them. 

